1. Field of the Invention
The invention relates to a method of forming copper interconnects.
2. Background of the Invention
Electromigration can lead to considerable material transport in metal films, and electromigration-induced failure is one the most important modes of failure in metal lines in Very Large Scale Integration (VLSI) circuits. The directional mobility of atoms are enhanced by the presence of grain boundaries, dislocation, and point defects in metal films. In the case of aluminum, electromigration leads to a transport and accumulation of aluminum in the direction of electron flow, resulting in discontinuities in the metal lines. Electromigration resistance in aluminum can be improved by the addition of copper, e.g., between about 0.5% to about 1%, to the aluminum films. It is believed that copper addition results in a change in the texture of aluminum films and an increase in the activation energy for aluminum self-diffusion, which in turn results in an improvement in electromigration resistance.
Copper has gained increasing popularity as a metal interconnect in advanced integrated circuit fabrication. Despite its significantly higher electromigration resistance compared to aluminum, there is an ongoing need to provide methods for improving electromigration resistance in copper interconnects.
The invention generally provides a method of forming a copper layer having improved electromigration characteristics. According to embodiments of the invention, a doped copper layer is formed by controlling an amount of a non-metal dopant incorporated in the doped copper layer. In one embodiment, the non-metal dopant is carbon, and the doped copper layer is formed by electroplating.